Electrolytic preparation of perchlorates



United States Patent Ofi 3,493,478 Patented Feb. 3, 1970 3,493,478ELECTROLYTIC PREPARATION OF PERCHLORATES Handady V. K. Udupa, SrinivasaSampath, Kapisthalam C. Narasimham, and Muthia Nagalingam, all CentralElectrochemical Research Institute, Karaikudi, (S. Rl y.), India;Chakkalakkal J. Raju, Fertilizer Corporation of India Ltd., TrombayUnit, Bombay, India; and Govinda Rao, Madras Rubber Factory,Tiruvottiyur, Madras, India N Drawing. Filed Dec. 2, 1966, Ser. No.598,609

Int. Cl. B01k 1/00; C01b 11/26, 11/18 US. Cl. 20482 11 Claims ABSTRACTOF THE DISCLOSURE Sodium perchlorate is prepared electrolytically fromsodium chloride solutions in one step by passing a direct currentthrough the solution, in the presence of fluoride ion. A stainless steelcathode and a lead dioxide anode are satisfactory.

This invention relates to the electrolytic preparation of perchloratesdirectly from sodium chloride using lead dioxide anode.

Hitherto it has been the practice to employ a twostage process for theproduction of perchlorates from chlorides, the first stage being theoxidation of chloride to chlorate using graphite, magnetite or leaddioxide anodes and the second stage consisting of the oxidation ofchlorate to perchlorate, using platinum or lead dioxide anodes. Thisconventional process has various drawbacks, such as: (i) that in betweenthe two stages the solutions have to be processed to isolate thechlorate and recover the unconverted chloride; (ii) that graphite getsdisintegrated to a considerable extent and magnetite to a lesser extentwhen used in the production of chlorates; and (iii) that there is aninevitable loss of platinum due to corrosion in the perchlorate cell.

With a view to avoiding the intermediate step of the processing theliquors after. the said first stage of the conventional process, it hasbeen proposed that the effluent from the chlorate cell should be treatedunder different electrolytic conditions from those in which the sodiumchloride solution was treated in the chlorate cell during the firststage of the process. But this proposed process also is a two stageprocess and the processing of the eflluent from the chlorate cellintroduces complications in the method.

This invention has for its main object an improved method which willobviate the drawbacks of known methods, and whereby the perchlorates maybe prepared directly from sodium chloride in a single step ofelectrolytic oxidation, the conditions of electrolysis being maintainedconstant at predetermined levles throughout the period. Another objectof this invention is to avoid the use of graphite, magnetite or platinumas the anode.

With these and other objects in view, this invention broadly consists ofa process of preparing sodium perchlorate directly from sodium chloridein a single step of electrolytic oxidation, which consists in passing adirect current through a bath of sodium chloride solution containingfluoride ions.

The improved process according to this invention may be carried out intopractice under the following conditions:

(i) The said fluoride ions may be provided by adding sodium fluoride orhydrogen fluoride to the bath.

(ii) About 0.5 to 5 g./l. of sodium fluoride may be added; but about 2g./l. would give satisfactory results.

(iii) The electrolytic oxidation may be carried out in a cell having astainless steel cathode and a lead dioxide anode.

(iv) The said anode may consist of massive lead dioxide or an electrodehaving lead dioxide electrodeposited on a substrate like graphite.

(v) The current density may range from 5 to 40 amp/dm.

(vi) The electrolytic oxidation may be carried out at a temperature of30 to 60 C.

(vii) The process may be carried until all the chloride is convertedinto perchlorate, the conditions of electrolysis being maintainedconstant at predetermined levels throughout the process.

The following Table I gives the particulars of three different examplesillustrating the invention:

TABLE I Example I II III Concentration of electrolyte (initial) (g. NaCl0 8 291 308. 1 Addition agents N 9.13 (g./l) 2 2 2 Anode Cathode Currentdensity (amp./dm. 10 25 19 Current concentration (amp./l) 18. 25 10Temperature of electrolyte C 40 45 Cell voltage (volts) 3. 0-3. 9 3.7-4. 5 3. 9-4. 5 Current etficiency percent 52. 2 53. 2 57. 5 Energyconsumption (kWh/kg. of

NaClOr) 13. 3 13. 9 13.2 Current passed (amps.) 15 20 800 Duration (hrs)78 223 Quantity of sodium perchlorate present in solution (gms) 544 5464 61. 0

1 Carbon substrate lead dioxide.

2 Graphite substrate lead dioxide. 3 Stainless steel.

4 Kgs.

The following Table II shows other beneficial effects resulting from theaddition of fluoride to the bath.

1 Graphite substrate lead dioxide. 2 Stainless steel.

Although this invention has been particularly described with referenceto the preparation of sodium perchlorate, it is to be understood that itis applicable also to the preparation of other perchlorates by theconversion of the sodium perchlorate prepared by this process, into therequired perchlorates by processes already known for such conversion.

What we claim is:

1. A process of preparing sodium perchlorate directly from sodiumchloride in a single step of electrolytic oxidation, which consists inpassing a direct current through a bath of sodium chloride solutioncontaining fluoride ions.

2. A process as claimed in claim 1, wherein the said fluoride ions areprovided by adding hydrogen fluoride to the said bath.

3. A process as claimed in claim 1, wherein the electrolytic oxidationis carried out using a current density range of 5 to 40 amp./dm.

4. A process as claimed in claim 1, which is carried out at atemperature of 30 to 60 C.

5. A process as claimed in claim 1, wherein the conditions ofelectrolysis are maintained constant at predetermined levels throughoutthe process.

3 6. A process as claimed in claim 1, wherein the said fluoride ions areprovided by adding sodium fluoride to the said bath.

7. A process as claimed in claim 6, wherein about 0.5 to 5 g./1. ofsodium fluoride is added to the sodium 5 chloride solution.

8. A process as claimed in claim 7 wherein the sodium fluoride added isabout 2 g./ 1.

9. A process as claimed in claim 1 wherein the electrolytic oxidation iscarried out in a cell having a stainless steel cathode and a leaddioxide anode.

10. A process as claimed in claim .9, wherein the said anode consists ofmassive lead dioxide.

11. A process as claimed in claim 9, wherein the said 4 anode consistsof an electrode having lead dioxide electro-deposited on a substratelike graphite.

References Cited UNITED STATES PATENTS 2,813,825 11/1957 Miller et a120482 2,840,519 6/1958 Stern et al. 204-S2 2,872,405 2/1959 Miller eta1. 204-290 3,020,124 2/1962 Bravo et a1. 20482 XR JOHN H. MACK, PrimaryExaminer D. R. JORDAN, Assistant Examiner U.S. C1. X.R. 20495

